1. Technical Field
The disclosure relates to acrylic copolymers with high heat-resistance and low water absorptivity.
2. Description of the Related Art
An optical acrylic polymer material can be widely used in various applications, such as light guiding plates (LGP), PDP front plates, optical diffusion plates or optical discs due to its high transparency, low birefringence, strong weather resistance and lower cost than other materials. Optical acrylic polymer materials, however, suffer from some drawbacks, such as low heat resistance and high water absorptivity. Thus, development of an improved acrylic polymer material is desirable.
Some methods for improving the heat resistance of PMMAs have been developed, for example, copolymerizing an MMA with an α-methylstyrene (U.S. Pat. No. 3,135,723), copolymerizing an MMA with a maleic anhydride (JP 49-10156), copolymerizing an MMA with a maleimide (JP 61-95011), crosslink-copolymerizing an MMA with a polyfunctional monomer (JP 63-30510) and copolymerizing a primary amine with a methacrylic resin to prepare a methacrylimide-containing polymer (JP 61-64703). Although the heat resistance thereof is improved, some drawbacks, such as slowing of the copolymerization rate, forming of color polymers and reduction in transparency still exist.
Meanwhile, some methods for reducing the water absorptivity thereof have been developed, for example, copolymerizing an MMA and a cyclohexyl methacrylate (JP 58-5318) and copolymerizing an MMA and a benzyl methacrylate (JP 58-13652). Although the water absorptivity thereof is reduced, heat resistance thereof is deteriorated. Thus, development of an optical polymer resin material with high thermal stability and low water absorptivity is desirable.